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package jiuzhang.java.elementary;

//Binary Tree Path Sum

import java.util.ArrayList;

import java.util.List;

public class BinaryTreePathSum {

public List<List<Integer>> binaryTreePathSum(TreeNode root, int target) {

if (root == null ) {

return new ArrayList<>();

}

// if (target < root.val) {

// return new ArrayList<>();

// }

if (root.left == null && root.right == null) {

if (target == root.val) {

ArrayList<Integer> aList = new ArrayList<>();

aList.add(root.val);

List<List<Integer>> halfResult = new ArrayList<>();

halfResult.add(aList);

return halfResult;

} else {

return new ArrayList<>();

}

}

List<List<Integer>> result = new ArrayList<>(binaryTreePathSum(root.left, target - root.val));

result.addAll(binaryTreePathSum(root.right, target - root.val));

for (List<Integer> aList : result) {

aList.add(0, root.val);

}

return result;

}

// List<List<Integer>> list = new ArrayList<List<Integer>>();

// or since Java 1.7

//

// List<List<Integer>> list = new ArrayList<>();

//what after new must be a class, cannot be an interface,

// what inside <> must be a type or an Interface

// you can cast a class to one of the interfaces it implements but

// not the other way,

// ArrayList<ArrayList<Integer>> cannot be converted to List<List<Integer>>

}